The present study is designed to gain insight into the nature of membrane-microtubule interactions and of the mechanism of membrane-associated motility. A new system of rapid motility occurring in association with the extracellular surface of Chlamydomonas flagella has been discovered. This system will be exploited using a combination of genetic, immunological, biochemical, and ultrastructural approaches in order to learn the nature of 1) the membrane surface receptor sites, 2) the contractile proteins associated with the cytoplasmic surface of the flagellar membrane, and 3) the manner by which mechano-chemical transduction occurring in the cytoplasmic surface of a membrane can result in work being performed at the extracellular surface of the membrane. A new assay has been developed and tested for detecting and quantitating the interaction of microtubules with membranes in vitro. This radioactive assay will be used in conjunction with electron microscopy to study the interaction of microtubules with the cytoplasmic surfaces of plasma membranes and organelle membranes and to determine the role of microtubule-associated proteins (MAPs) in these interactions.